Encontrei a resposta na novelização de Alan Dean Foster (todas as citações são ali, salvo indicação em contrário).
Não todos entendem o BB-8. Finn não . Então é plausível que Rey - sendo um scavenger mecanicamente talentoso - tenha aprendido Binary ( UPDATE : Os dados do TFA Visual Dictionary incluem explicitamente um trecho que Rey teve contato com pessoas fora do mundo e aprendeu binário deles ).
“Okay, look—we have to know the location of the Resistance base. You heard Rey. She thinks she can get us there—but you have to tell us where it is.” The droid emitted a flurry of rapid, soft beeps. An impatient Finn waved them off.
“I don’t speak that, but I think I got the gist. You just accused me of not being with the Resistance, didn’t you?”
Esta teoria é confirmada, porque Chewie pode falar com o BB-8:
Striding effortlessly alongside, Chewbacca groaned assent. Behind Finn, BB-8 beeped a question to which the Wookiee readily replied. Droid and Wookiee then entered into a rapid-fire conversation, the sound of which made Finn’s head hurt.
Obviamente, Poe - que era um piloto com o BB-8 como seu astromech, era um bom candidato para entendê-lo. Sim.
“I wasn’t dead, just momentarily out of it,” the pilot explained. “Came around long enough to see that you had got out. Pulled out of the dive just long enough to set down—hard. Impact threw me clear. Woke up at night; no you, no ship, no nothing. Went looking—in the wrong direction. Got picked up by some itinerant trader.” He grinned. “Tell you all about it sometime.” A plaintive beep caused him to turn and look down. “Beebee-Ate says that you saved him.”
No entanto, sabemos que quase ninguém entende o R2-D2: o Luke mal faz (ele precisa da tradução do X-Wing no canon); Leia não entende R2-D2 em TFA (e nem, aparentemente, Poe que traduz para BB-8, mas não R2-D2, que precisa da tradução de C-3PO)
An excited Leia moved closer. Of all the organics in the room, no one had a more personal relationship to the little droid than she did.
“What’s he saying?” she asked.The protocol droid explained. “If the information you are seeking was in the Imperial archives, he believes he may have cataloged that data. He’s scanning through it now.”
Rey stared at the diminutive droid. “Artoo has the rest of the map?”
“He’s certainly implying the possibility!” C-3PO told her. “I’ve never heard him beep with this much energy before.”Emitting a long, sustained whistle, R2-D2 projected a full three-dimensional image of a huge navigational star chart. No one in the room could fail to notice that it was missing a substantial fragment. In response to the hovering image, BB-8 began beeping excitedly. “Yeah, buddy, hold on,” Poe told him. “I have it.”
Agora, isso não explica o como .
No entanto, sabemos por ocasião da novelização que o BB-8 falou DIFERENTES linguagens de dróides - talvez uma variante fosse mais compreensível para os orgânicos?
In the dark, dusty storeroom he rolled over to the R2 unit and beeped a greeting, the transmission sequence too rapid and too exhaustive for any human to follow. It didn’t matter. There was no response from the immobile R2 unit.
BB-8 tried again, utilizing a different droid language. When that also failed, he moved forward and gave the other mechanical a forceful nudge. Like everything else, that too failed to generate a response.
Sabemos também que a sua língua materna está relacionada com o padrão Binary, mas é uma geração mais evoluída, o que pode explicar muito por que muitas pessoas a entendem.
27th generation droid-speak code, a compressed variant of the most common astromech language (source: TFA Visual Dictionary, or SFF.SE)